KR20070108224A - Process for inhibiting deposition of solids derived from gas stream obtained from hydroformylation reaction mixture - Google Patents

Abstract

The present invention relates to a method of degassing an aqueous solution containing a hydroformylation product and separating volatile metal species from the gas stream in order to inhibit or prevent the deposition of solid material from a gas stream. In order to separate the volatile metal species from the gas stream, the gas stream is contacted with 1) a liquid that separates the volatile metal species or reaction products thereof from the gas stream; 2) passing through a microfilter having a pore size of 2 μm or less; Or 3) contact with adsorbent material.

Description

PROCESS FOR INHIBITING DEPOSITION OF SOLIDS FROM A GASEOUS STREAM OBTAINED FROM A HYDROFORMYLATION REACTION MIXTURE}

The present invention relates to a method for inhibiting or preventing the deposition of solid material from a gas stream. More particularly, the present invention relates to a method for inhibiting or preventing the deposition of solid material from a gas stream obtained by at least partial degassing of an aqueous mixture separated in a hydroformylation reaction mixture.

1,3-propanediol (PDO) is an industrially important chemical. PDO is used as monomer unit to form polymers such as poly (trimethylene terephthalate) used in the production of carpets and textiles. PDOs are also useful as engine coolants, particularly in cooling systems that require coolants with low conductivity and low corrosiveness.

PDO can be produced industrially by hydroformylation of ethylene oxide under pressure and catalyst in the presence of syngas (CO and H ₂ ) to produce 3-hydroxypropionaldehyde (HPA), followed by hydrogenation of HPA with PDO. Preferred hydroformylation catalysts are metal carbonyls, in particular cobalt carbonyl. Hydroformylation reactions are usually carried out in solvents that are inert to the reactants, dissolve carbon monoxide and catalysts, are almost immiscible in water, and have low or moderate polarity, thus extracting the hydroformylation product HPA from the solvent with water. I can do it. Such solvents include ethers such as methyl-t-butyl ether (MTBE), ethyl-t-butyl ether, diethyl ether, phenylisobutyl ether, ethoxyethyl ether, diphenylether and diisopropyl ether.

After hydroformylation, HPA is extracted with water and separated from water immiscible solvents. The separated HPA aqueous solution is then hydrogenated in the presence of a hydrogenation catalyst to form PDO. The organic phase containing most of the metal carbonyl catalyst and the hydroformylation reaction solvent can be recycled and reused for further hydroformylation.

The separated HPA aqueous solution can be treated to remove species that may interfere with the performance of the hydrogenation catalyst when converting HPA to PDO. The separated HPA aqueous solution generally contains 4 to 60 wt% HPA, residual syngas (including carbon monoxide), residual ethylene oxide, and residual metal carbonyl species derived from hydroformylation reaction catalysts, such as cobalt or rhodium carbonyl species, such as Co [Co (CO) ₄ ] ₂ , Co ₂ (CO) ₈ and Rh ₆ (CO) ₁₆ . Most hydrogenation catalysts are poisoned by carbon monoxide (CO) and residual metal carbonyl species, so an aqueous HPA solution is treated to remove the catalyst poison from this solution. The aqueous HPA solution may be degassed, oxidized and stripped and then contacted with an acidic ion exchange resin to remove the hydrogenation catalyst poison source.

The aqueous HPA solution can be degassed, oxidized and stripped by passing an oxygen containing gas through a column or tank of HPA aqueous solution, usually in a countercurrent arrangement. The pressure maintained in the HPA aqueous solution in such degasser-oxydizer-stripper column or tank is usually lower than the pressure in hydroformylation reaction and extraction, so that CO The gas is vented and any residual CO gas is removed from the solution using any other stripping gas stream such as nitrogen and an oxygen containing gas.

In addition, the oxygen-containing gas oxidizes the residual metal carbonyl species in the aqueous solution, making the metal species surely water soluble, especially in the presence of organic acid by-products such as 3-hydroxypropionic acid in HPA aqueous solution. Water soluble metal species are removed from the aqueous solution by contacting the acidic ion exchange resin with an aqueous HPA solution.

The gas stream containing degassed CO may be removed from a degasser-oxydizer-stripper tank or column separating the CO from the aqueous HPA solution. The gas stream removed from the degasser- oxidizer-stripper is generally collected and condensed to recover any residual hydroformylation solvent contained therein. Recovery of the solvent from the gas stream is important to reduce the environmental impact, for example residual solvent MTBE cannot be discharged directly to the atmosphere because it is a regulated pollutant. The gas stream from the degasser-oxydizer-stripper can be compressed using a compressor and the solvent can be recovered by cooling the compressed gas in a cooling tank.

Unexpectedly, it has been found that the deposition of solids from a gas stream inhibits the effective recovery of solvent from the gas phase. For example, if gas compression is used for solvent recovery, solids precipitate in the compressor and contaminate the compressor. As a result, the compressor is only operated for a short time before it is blocked by precipitated solids. The degasser- oxidizer-stripper and other process parts must then be shut down to clean or replace the compressor, which reduces process efficiency, especially in industrial continuous operation. Moreover, blockage by deposited solids causes the compressor to suffer excessive wear. Similar contamination by solids deposited from the gas stream can also be observed in other solvent recovery configurations such as liquid recovery, distillation, cold condensation or solvent recovery by solids adsorption.

Summary of the Invention

The present invention provides a gas obtained in an aqueous mixture separated from a hydroformylation reaction mixture, comprising separating volatile metal species from the gas stream obtained by at least partial degassing of the aqueous mixture separated in the hydroformylation reaction mixture. Provided are methods for inhibiting or preventing the deposition of solids from streams. According to one aspect of the invention, the volatile metal species are separated from the gas stream by contacting the gas stream with the capture liquid. According to another aspect of the present invention, volatile metal species are separated from the gas stream by passing the gas stream through a filter having a pore size of 2 μm or less. According to another aspect of the invention, the volatile metal species are separated from the gas stream by contacting the gas stream with the adsorbent solids.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a degasser-oxydizer-stripper column used according to the method of the present invention.

2 is a schematic diagram of a degasser-stripper-oxidizer column and a scrubber used in accordance with the method of the present invention.

The present invention provides a method for inhibiting and / or preventing the deposition of solid material from a gas stream obtained by at least partially degassing an aqueous mixture separated from a hydroformylation reaction mixture. The presence of a component that precipitates as a solid in such a gas stream at or near ambient temperature, and at or near atmospheric pressure is such that the gas stream contains mostly stripping gases such as carbon monoxide and air and nitrogen from aqueous mixtures. It was unexpected. It has been found that volatile metal species are present in the gas stream and such volatile metal species or reaction products thereof precipitate out of the gas stream as a solid material. However, a volatile metal species gas stream is generated from an aqueous mixture containing only very small amounts of metal species and substantially remaining in the metal species aqueous mixture when the aqueous mixture is degassed, oxidized and stripped to form a gas stream. It was unexpected to be present in an amount sufficient to precipitate any substantial amount of solids.

Some residual metal carbonyl catalyst from the hydroformylation reaction mixture that is separated from the aqueous mixture used to extract the hydroformylation reaction mixture can be collected as volatile metal species in the gas stream upon degassing, oxidation and stripping of the aqueous mixture, It has been found that these volatile metal species or reaction products thereof will precipitate out as solids from the gas stream. For example, cobalt hydridocarbonyl (HCo (CO) ₄ ) is formed from incomplete oxidation of the cobalt imbalance salt Co [Co (CO) ₄ ] ₂ in the presence of a small amount of acid, a coproduct from the hydroformylation step and It is a highly volatile species that collects in a gas stream that is separated from a degasser- oxidizer- stripper tank or column when the HPA aqueous mixture is degassed, oxidized and stripped.

The present invention provides a process for removing one or more volatile metal species, in particular volatile metal carbonyl and hydridocarbonyl, from a gas stream obtained by at least partially degassing an aqueous mixture separated from a hydroformylation reaction mixture. Although the term "volatile metal species" as used below refers to a single substance, the expression "volatile metal species" should be understood to include one or more volatile metal species.

The aqueous mixture preferably contains at least one metal species derived from the carbonylation catalyst and the hydroformylation product. Most preferably, the aqueous mixture is an aqueous solution obtained when the hydroformylation reaction mixture is extracted with water to separate the hydroformylation reaction product, preferably HPA, from the hydroformylation reaction mixture. Such aqueous mixtures may be aqueous slurries or aqueous solutions containing at least 40% water by weight.

The volatile metal species is contacted with a liquid for wet cleaning the gas stream and the gas stream and then the gas stream is filtered with a filter having a pore size of 2 μm or less, or the gas stream is contacted with a suitable solid adsorbent, preferably molecular sieve. Can be separated from the gas stream. The separated gas stream can be further treated without volatile metal species or reaction products thereof that deposit as solid material from the gas stream.

The aqueous mixture from which the gas stream is generated contains the metal species and hydroformylation products from the carbonylation catalyst. According to a preferred embodiment, the metal species is an unbalanced salt of metal carbonyl, most preferably an unbalanced salt of cobalt and / or rhodium carbonyl, and the carbonylation catalyst is metal carbonyl, most preferably cobalt and / or rhodium Carbonyl. Most preferably, the hydroformylation product in the aqueous mixture is HPA.

The aqueous mixture comprises the steps of 1) producing a water soluble hydroformylation product using a carbonylation catalyst which hydroformylates an unsaturated carbon compound in the presence of syngas in an essentially non-miscible solvent; 2) extracting the solvent with water or an aqueous extractant which is a water containing a solution incompatible with the hydroformylation reaction solvent to extract a water-soluble hydroformylation product and a metal species derived from a carbonylation catalyst from the solvent; And 3) separating the aqueous extractant containing the metal species derived from the solvent and the hydroformylation product to obtain an aqueous mixture. In the most preferred embodiment, the unsaturated carbon compound is ethylene oxide (EO) and the hydroformylation product is HPA.

To hydroformyl the unsaturated carbon compound, the separation or mixed feed stream of the unsaturated carbon compound and CO and H ₂ (syngas) may be a pressure reaction vessel such as a bubble column or a stirred tank operating in batch or continuous mode. In a hydroformylation vessel. Hydrogen and carbon monoxide may be added to the reaction vessel generally in a molar ratio in the range from 1: 2 to 8: 1, preferably in the molar ratio in the range from 1: 1 to 6: 1. The feed stream is contacted in the presence of a carbonylation catalyst, generally a catalyst selected from metal carbonyl, preferably rhodium and / or cobalt carbonyl. The carbonylation catalyst may be present in the reaction mixture in an amount usually in the range of 0.01 to 1.0 wt%, preferably in the range of 0.05 to 0.5 wt%, based on the weight of the hydroformylation reaction mixture.

The hydroformylation reaction is carried out under conditions effective to produce a hydroformylation reaction product mixture containing a significant amount of the desired hydroformylation product in which the desired hydroformylation product is substantially water soluble. The expression "substantially water soluble" as used herein is defined as being at least 40 wt% soluble in water. In a preferred embodiment, the reaction is carried out under continuous process conditions that are effective to produce a hydroformylation reaction product mixture wherein substantially the water soluble hydroformylation product is HPA and the amount is HPA and a small amount of acetaldehyde and PDO. The level of HPA in the mixture is maintained in the range of less than 15 wt%, preferably in the range of 3 to 10 wt% (to provide solvents with different densities, the preferred concentration of HPA in the reaction mixture is a molar concentration, ie less than 1.5 M, preferably 0.5 to 1M range).

In general, the cobalt carbonyl catalyzed hydroformylation reaction can be carried out at elevated temperatures in the range of less than 100 ° C., preferably 60 ° C. to 90 ° C., most preferably 70 ° C. to 85 ° C., and rhodium carbonyl catalysis. The hydroformylation reaction can be carried out at about 10 ° C. or higher. The hydroformylation reaction can generally be carried out at a pressure in the range of 3 to 35 MPa, more preferably at a pressure in the range of 7 to 25 MPa (for economical processes), with higher pressures being preferred to increase reaction selectivity.

The hydroformylation reaction is preferably carried out in a liquid solvent that is inert to the reactants. "Inert" means that no solvent is consumed during the reaction process. In general, the ideal solvent for the hydroformylation process dissolves carbon monoxide, is essentially non-water miscible, and has a low or moderate polarity such that the hydroformylation product can be dissolved at a desired concentration of at least 5 wt% under hydroformylation conditions. While the significant solvent is one that can be retained as the separation phase upon water extraction. The expression “essentially non-water miscible” means having a solubility of less than 25 wt% in 25 ° C. water, such that it forms a separate hydrocarbon rich phase upon water extraction of the hydroformylation product from the hydroformylation reaction mixture.

Preferred types of solvents include ethers and alcohols which can be represented by the formula:

R ₂ -OR ₁

Wherein R ₁ is hydrogen or C _1-20 linear, branched, cyclic or aromatic hydrocarbon or monoalkylene or polyalkylene oxide, and R ₂ is C _1-20 linear, branched, cyclic or aromatic hydrocarbon, alkoxy Or monoalkylene or polyalkylene oxides. Most preferred hydroformylation solvents are ethers such as methyl-t-butyl ether, ethyl-t-butyl ether, diethyl ether, phenylisobutyl ether, ethoxyethyl ether, diphenyl ether and diisopropyl ether. It is also possible to use solvent blends such as tetrahydrofuran / toluene, tetrahydrofuran / heptane and t-butylalcohol / hexane to obtain the desired solvent properties. Due to the high yield of HPA usually obtainable under reaction conditions, the presently preferred solvent is methyl-t-butyl ether.

In order to further improve the yield under normal reaction conditions, it will be desirable to add a catalyst promoter to the hydroformylation reaction mixture to promote the reaction rate. Preferred promoters are lipophilic phosphonium salts and lipophilic amines that accelerate the rate of hydroformylation without imparting hydrophobicity (water solubility) to the active catalyst. As used herein, the term "lipophilic" means that the co-catalyst tends to remain in the organic phase after extraction of the hydroformylation reaction mixture with water. The cocatalyst may generally be present in an amount ranging from 0.01 to 1.0 mole per mole of metal component of the catalyst (eg cobalt or rhodium carbonyl). Presently preferred lipophilic promoters are tetrabutylphosphonium acetate and dimethyldodecyl amine.

Water at low concentrations acts as a promoter of the preferred carbonyl catalytic species formation. The level of water most suitable for hydroformylation in methyl-t-butyl ether solvent is within the range of 1 to 2.5 wt%. However, excess water can lower the selectivity for the desired hydroformylation product to below acceptable levels and lead to the formation of a second liquid phase.

After the hydroformylation reaction, the hydroformylation reaction mixture containing the hydroformylation product, preferably HPA, the reaction solvent, the carbonylation catalyst, the residual syngas, the residual unsaturated carbon compound and the small amount of byproducts, is cooled down to an aqueous liquid. Transfer to extraction vessel for extraction. An aqueous liquid, generally water and an optional blending solvent, are used to extract the hydroformylation reaction product mixture and are separated from the hydroformylation reaction solvent after extraction to provide an aqueous mixture for use in the process of the invention.

Aqueous extraction may be carried out by any suitable means capable of pressurized extraction, such as mixer-settlers, packed or trayed extraction columns or rotary disk contactors and the like. The amount of water added to extract the hydroformylation reaction mixture may be such that it provides a ratio of the water-mixture generally in the range of 1: 1 to 1:20, preferably in the range of 1: 5 to 1:15. Extraction with relatively small amounts of water can provide an aqueous mixture having more than 20 wt%, preferably more than 35 wt% and preferably up to 60 wt% of hydroformylation products, which allows for economic hydrogenation of the hydroformylation product.

The aqueous extraction is preferably carried out at a temperature in the range from 25 ° C. to 55 ° C., with lower temperatures being preferred. Importantly, aqueous extraction is carried out under constant pressure of syngas. Extraction at 25 to 55 ° C. under partial pressure in the range of 0.4 to 7 MPa carbon monoxide maximizes the carbonylation catalyst residual in the organic phase and minimizes the content of carbonylation catalyst in the aqueous mixture that is ultimately separated from the aqueous phase. Extraction can be carried out under a total pressure of 1-25 MPa of syngas.

After extraction, the aqueous phase is separated from the non-miscible phase according to the procedures of the liquid-liquid phase separation pass to obtain an aqueous mixture containing the metal species derived from the carbonylation catalyst and the hydroformylation product. This aqueous mixture preferably contains a reaction product derived from cobalt and / or rhodium carbonyl, such as hydroformylation product HPA and small amounts of cobalt or rhodium carbonyl, or an unbalanced salt of cobalt or rhodium carbonylation. The non-water miscible phase generally retains most of the carbonylation catalyst derived from the hydroformylation reaction and is preferably recycled for use in the hydroformylation reaction again.

After separating the aqueous mixture containing the hydroformylation product and the metal species derived from the carbonylation catalyst from the non-water miscible phase, the aqueous solution is at least partially degassed, preferably completely degassed to contain a gas containing volatile metal species. Create a stream. Volatile metal species are likely to be derived from the metal species of the carbonylation catalyst. The volatile metal species may be metal carbonyl or metal hydridocarbonyl, most preferably cobalt or rhodium carbonyl or cobalt or rhodium hydridocarbonyl. The gas stream generally contains residual hydroformylation solvents that were previously loaded on carbon monoxide, syngas and the aqueous mixture.

The aqueous mixture can be degassed by lowering the pressure on this aqueous mixture. The aqueous mixture is preferably degassed when the aqueous mixture is removed from the extraction apparatus by lowering the pressure on the aqueous mixture to a pressure below the pressure used during the aqueous extraction. Most preferably, the pressure drop is a pressure drop large enough to instantaneously evaporate volatiles from the aqueous mixture, such as carbon monoxide, volatile metal species residual loaded hydroformylation solvent, and any other gases, such as residual syngas. According to a preferred embodiment, the extraction is carried out under a pressure of 1 to 25 MPa of syngas or carbon monoxide and the aqueous mixture is degassed at a pressure of 0.2 MPa or less, most preferably less than 0.15 MPa. The flow rate of gas generated relative to liquid depends on the amount of gas dissolved in the aqueous mixture under extraction conditions, and the higher the pressure, the greater the concentration of dissolved gas.

The aqueous mixture may be stripped when degassed to more completely remove some of the residual carbon monoxide, volatile metal species and residual hydroformylation solvent. The aqueous mixture may be stripped by injecting or foaming an inert gas into the aqueous mixture to help remove other gases from the aqueous mixture. The aqueous mixture is preferably stripped by injecting or foaming nitrogen gas through the aqueous mixture. Any flow rate of the stripping gas relative to the aqueous liquid flow rate can be used to increase the removal of dissolved syngas from the aqueous mixture above the amount removed via "flashing" to lower the pressure. Most typically, a flow rate ratio of 5-20 mol / hour of liquid per mol / hr of stripping gas may be used. In the most preferred embodiment, the stripping gas is contacted with the aqueous mixture in countercurrent.

According to the most preferred embodiment, the aqueous mixture is preferably treated with an oxidizing agent when degassing and stripping. The oxidant preferably oxidizes the metal species derived from the carbonylation catalyst in the aqueous mixture and the volatile metal species in the gas stream. Most of the oxidized metal species present and soluble in the aqueous mixture can be removed from the aqueous mixture by passing it through an acidic ion exchange resin before passing the aqueous mixture through a hydrogenator for hydrogenation. Removal of the metal species from the aqueous mixture with ion exchange resins ensures that the hydrogenation catalyst is not poisoned with the metal species during subsequent hydrogenation of the hydroformylation product in the aqueous mixture. Oxidation of volatile metal species present in the gas stream can be made into compounds that are easier to separate from the gas stream.

In one aspect, the aqueous mixture and gas stream may be treated with an oxidizing gas that oxidizes the metal species derived from the carbonylation catalyst present in the aqueous mixture and the volatile metal species present in the gas stream. The oxidizing gas is preferably an oxygen-containing gas, most preferably air. In addition, the aqueous mixture is preferably treated with the oxidizing gas by contacting the oxidizing gas with the aqueous mixture in countercurrent. The aqueous mixture is composed of the majority, preferably almost all, of the metal species derived from the carbonylation catalyst present in the aqueous mixture, and most, preferably almost all, of the volatile metal species present in the gas stream degassed from the aqueous mixture. Preference is given to treating with an amount of oxidizing gas effective to oxidize the species. Most preferably, the oxidizing gas is diluted with an inert component such as nitrogen which keeps the composition outside the combustible range of the final gas mixture. Preferred operation is to use a mixed stripping and flow rate ratio of 5-20 mol / hr of aqueous liquid per mol / hr of oxidizing gas. The concentration of oxygen present in the stripping gas is preferably less than 5 mole percent to avoid flammability of the composition.

In another embodiment, the aqueous mixture and gas stream may be treated with an oxidizing liquid that oxidizes the metal species derived from the carbonylation catalyst present in the aqueous mixture and the volatile metal species present in the gas stream. Such oxidizing liquid is preferably nitric acid or hydrogen peroxide. The aqueous mixture and the gas stream can be treated countercurrently with the oxidizing liquid or by mixing with the aqueous mixture. The aqueous mixture is preferably most of the metal species derived from the carbonylation catalyst present in the aqueous mixture, preferably almost all metal species, and most, preferably almost all of the volatile metal species present in the gas stream degassed from the aqueous mixture. It is treated with an oxidizing liquid in an amount effective to oxidize all metal species. In general, this can be done by supplying a stoichiometric excess of oxidant content to the total moles of metal species present in the aqueous mixture prior to degassing and stripping treatment.

The inventors believe that the contact of the oxidant with the aqueous mixture causes a small amount of metal species derived from the carbonylation catalyst present in the aqueous solution to become volatile and enter the gas stream. For example, the cobalt imbalance salt Co [Co (CO) ₄ ] ₂ may be present in the aqueous mixture from the cobalt carbonyl catalyst used as hydroformylation catalyst in hydroformylation of ethylene oxide to HPA. This cobalt imbalance salt is in equilibrium with volatile cobalt hydridocarbonyl HCo (CO) ₄ in the presence of 3-hydropropionic acid present in the aqueous mixture as a byproduct of the hydroformylation reaction. This equilibrium disadvantages the formation of strongly acidic cobalt hydridocarbonyl. However, oxidation and stripping of the aqueous mixture in the presence of stabilizing pressure of the carbon monoxide released can cause volatile cobalt hydridocarbonyl to escape from the gas stream, leading to the equilibrium towards the formation of cobalt hydridocarbonyl.

The temperature can be used as the temperature to optimize the oxidation of volatile metal species from the gas stream. The temperature may be raised during the oxidation step through the addition of steam, hot water or other means to accelerate the oxidation of the volatile components. The temperature at which the oxidant contacts the aqueous mixture and gas stream is preferably in the range of 50 to 100 ° C. which accelerates the oxidation of volatile metal species.

The aqueous mixture may be degassed in a conventional tank or column, which may receive pressurized liquid and discharge the gas stream as an exhaust gas and allow the degassed aqueous mixture to separate from the column or tank, and may be stripped and oxidized, if desired. . If desired, if the aqueous mixture is to be stripped and oxidized, the tank or column should have an inlet for injecting the stripping gas and the oxidizing gas or liquid into the aqueous solution.

Volatile metal species are separated from this volatile metal species gas stream and then from the gas stream produced by the degassing of the aqueous mixture in a manner effective to inhibit or prevent the deposition of solid material from the gas stream. In a preferred embodiment, the volatile metal species are contacted with a liquid or solid with a gas stream, and then separated from the gas stream by collecting the volatile metal species or reaction products thereof separated from the gas stream.

Liquids or solids for separating volatile metal species from the gas stream should be selected to be effective for removing volatile metal species from the gas stream. In one embodiment, volatile metal species are separated from the gas stream using an aqueous capture liquid that is soluble or an aqueous capture liquid that reacts to form a non-gas reaction product. Preferably the aqueous capture liquid is water, more preferably the aqueous capture liquid is an aqueous mixture which is optionally degassed, oxidized and stripped after extraction of the hydroformylation reaction mixture. If desired, the aqueous capture liquid is a basic solution, preferably an alkaline solution, such as potassium or sodium hydroxide. Volatile metal hydridocarbonyls, such as cobalt hydridocarbonyl, can be effectively removed from the gas stream by an aqueous mixture extracted from water or a hydroformylation reaction mixture, in particular volatile metal hydridocarbonyls are strongly acidic and react with base Thereby forming a salt which is effectively removed from the gas stream by the aqueous basic solution. Typical flow rate ratios involve treatment with 2 to 100 parts by weight of gas per part of capture liquid.

In another embodiment, a liquid organic solvent in which the volatile metal species is soluble can be used to separate the volatile metal species from the gas stream. The liquid organic solvent is preferably MTBE. Volatile metal carbonyls that are not oxidized and are not salts, such as cobalt and rhodium carbonyl, can be effectively removed from the gas stream by MTBE. Organic solvents in which the volatile metal species are soluble can be most effectively used to separate volatile metal species from the gas stream when little or no aqueous mixture is oxidized. Typical flow rate ratios involve treatment of 2 to 100 parts by weight of gas with 1 part of capture organic liquid.

In a most preferred embodiment, after extraction of the hydroformylation reaction mixture, optionally degassed, oxidized and stripped aqueous mixture is used as a liquid capture agent to separate volatile metal species from the gas stream. This aqueous mixture is particularly preferred because it contains significant levels of organic compounds that can effectively remove volatile metal hydridocarbonyl and unoxidized volatile metal carbonyl from the gas stream.

Gas streams containing volatile metal species can be separated from the gas stream by contact with the capture liquid using conventional apparatus commonly used to contact and mix gas and liquid. In particular, the device used to contact the gas stream with the capture liquid is preferably easy to operate in the presence of solids. Solids may form when the volatile metal species in the gas stream are contacted with the liquid and separated from the volatile metal species gas stream.

In a preferred embodiment, a conventional commercial Venturi scrubber is used to contact the capture liquid with the gas stream to separate volatile metal species from the gas stream. Venturi scrubbers can be designed to accommodate various liquid / gas flow rates as well as solids that may be formed due to the capture of volatile metal species. Typically, the liquid flow rate can be planned to maintain a concentration of solids less than 1% of the total flow rate.

According to another preferred embodiment, a conventional commercial tray or plate column can be used to contact the gas stream containing the volatile metal species with the capture liquid to separate the volatile metal species from the gas stream. The capture liquid flow rate is preferably provided in an amount effective to maintain the concentration of the solids at about 1% or less. The flow rate of the gas stream in the column is preferably adjusted to provide a sufficient amount of liquid on the tray or plate such that the capture liquid and gas phase effectively contact. Knowing the expected flow rates of volatile metal species will allow the above conditions to be met simultaneously by variations in column diameter and tray or plate design. In addition to the foregoing, other means of contacting the gas stream with the capture liquid include spray towers, bubble columns, and packing columns.

In the most preferred embodiment, the aqueous mixture formed by the aqueous extraction of the hydroformylation reaction mixture is used as a capture liquid to separate volatile metal species from the gas stream after the aqueous mixture is degassed, stripped and oxidized. Most preferably the aqueous mixture is degassed, stripped, and oxidized in a plate or tray column and then recycled through a column which contacts the gas stream to separate volatile metal species from the gas stream.

The pressurized aqueous mixture obtained from the extraction of the hydroformylation reaction mixture is transferred centrally between the top and bottom of the degassing, stripping and oxidation columns to degas, strip and oxidize the aqueous mixture, thus degassing, stripping and oxidizing The aqueous mixture can be recycled to separate volatile metal species from the gas stream. The pressurized aqueous mixture is degassed upon entering the low pressure column. The off-gas stream formed by the degassing of the aqueous mixture moves upward through the column from the centrally located inlet zone to the top of the column. The degassed aqueous mixture moves downward from the central inlet zone to the bottom of the column. Air and nitrogen may be injected into the aqueous mixture at or near the bottom of the column, which is preferably arranged to move upward through the column in countercurrent to the downwardly moving aqueous mixture. Upon reaching the bottom or near the bottom of the column, part of the degassed, stripped and oxidized aqueous mixture is separated from the column and eluted through an acidic ion exchange resin to remove the oxidized water soluble metal species contained therein. It can be hydrogenated.

Degassing, stripping, and other portions of the oxidized aqueous mixture can be recycled from the bottom or near the bottom of the column to the top or near the top of the column, where the recycled aqueous mixture is from the top or near the top of the column to the bottom or bottom of the column. Move down through the column to the vicinity. The recycled aqueous mixture is contacted with an upwardly moving gas stream as it moves down the column. The recycled aqueous mixture acts as a capture liquid and separates volatile metal species from the gas stream. The gas stream may then be separated at the top of the column and treated to separate any residual hydroformylation solvent contained therein. Upon reaching the bottom of the column, the recycled aqueous mixture can be recycled again or separated from the column to elute and hydrogenate through an acidic ion exchange resin.

According to another aspect of the invention, the volatile metal species are also removed from the volatile metal species gas stream and then oxidized gas after oxidation of the gas stream in an effective manner to inhibit or prevent the deposition of solid material from the gas stream. The stream can be mechanically filtered to separate from the gas stream. Oxidation of the gas stream is preferably carried out in contact with an oxygen containing gas, preferably air. The filtration system may be an effective equipment for removing most, if not all, of volatile metal species or reaction products thereof from the oxidized gas stream. In one embodiment, the volatile metal species are separated from the gas stream by passing the oxidized gas stream through a filter having a pore size of 2 μm or less, preferably 1 μm or less. A preferred filter having a pore size of 1 μm or less is a commercial HEPA submicron filter made of glass wool.

In a particularly preferred embodiment, two or more filters in series are used to separate volatile metal species from the gas stream. At this time, the gas stream may be passed through a first filter having a pore size in the range of 2 to 4 μm and then through a final filter having a pore size of 1 μm or less, preferably a HEPA submicron filter made of glass wool. . Another filter may be used between the first filter and the final filter, wherein the other filter preferably has a pore size between the pore size of the first filter and the final filter.

According to a preferred embodiment, the filters are preferably washed at least intermittently while passing the gas stream through these filters. Intermittent washes are used to remove solids from the filter that are soluble in the washes and that can subsequently deposit on the filter upon separation of volatile metal species from the gas stream. Aqueous washing is preferred for washing the filter, with aqueous alkali washing being most preferred.

If a filter is used to separate volatile metal species or reaction products thereof from the gas stream, the filter should be located next to the gas outlet of the degassing column or tank where the gas stream is withdrawn from the degassing column or tank. Placing the filter directly adjacent to the gas outlet of the degassing tank or column ensures that the filter is volatile metal from the gas stream without depositing volatile metal species or reaction products thereof as solids in other process components such as connectors or compressors or coolers. Allows species or reaction products thereof to be separated.

According to the most preferred embodiment, the volatile metal species are separated from the gas stream by contacting the capture liquid with the gas stream as described above and then passing the gas stream through at least one mechanical filter as described above.

According to another aspect of the invention, the volatile metal species may be separated from the gas stream by contacting the gas stream with an adsorptive solid effective to adsorb the volatile metal species and / or reaction products thereof. Preferably, the gas stream is separated from the gas stream by passing the gas stream over a fixed bed of material effective to adsorb volatile metal species and / or reaction products thereof. Silica, alumina, or silica-alumina adsorbents, preferably molecular sieves, can be used for such applications. In a preferred embodiment, the material used in the fixed bed to adsorb volatile metal species and / or reaction products thereof is a commercial molecular sieve, preferably a molecular sieve 13X adsorbent. Passing a gas stream through a long bed length of adsorbent material is preferred to effectively separate volatile metal species from the gas stream rather than through a short bed. The appropriate bed length is passed through the bed at a particular flow rate of the gas stream to measure the amount of volatile metal species remaining in the gas stream, and then the bed length is selected to a bed length size that is optimal for removing volatile metal species from the gas stream. You can decide by adjusting.

Preferably, the gas stream oxidizes the volatile metal species prior to oxidizing and passing the gas stream over a fixed bed of adsorbent material to increase the amount of volatile metal species and / or reaction products thereof that are likely to be adsorbed onto the adsorbent material. Oxidation of the gas stream may be carried out by contacting the gas stream with an oxidant such as air or an oxidizing liquid, under conditions that provide a stoichiometric excess of oxidation relative to the content of volatile metal species to be removed, as described above.

The temperature can be used as the temperature that optimizes the removal of volatile metal species from the gas stream. If oxidation does not proceed fully, low temperatures are preferred to induce condensation in the liquid or on the adsorbent from the volatile metal species gas stream for subsequent capture or adsorption steps. For example, since the cobalt hydridocarbonyl has a boiling point of 47 ° C., it is preferable to use a capture liquid having a temperature of 40 ° C. or less in order to separate the cobalt hydridocarbonyl from the gas stream. In a preferred embodiment, if a cold capture liquid is used to separate volatile metal species from the gas stream, the temperature of the cold capture liquid is preferably between 5 and 15 ° C.

Referring now to FIG. 1, a preferred embodiment of carrying out the method of the present invention is presented. A carbon monoxide / syngas pressurized aqueous solution under a pressure of at least 1 MPa containing a metal species derived from a carbonylation catalyst, a hydroformylation product, carbon monoxide, syngas and residual organic solvent, was added to the top 15 of the DSO column 11 and the bottom. Inlet 13 located in the center between the 17 may be injected into the degasser-stripper-oxidizer (DSO) column (11). The aqueous solution is preferably an aqueous extract of a hydroformylation reaction carried out using a carbonylation catalyst, most preferably a cobalt carbonyl catalyst. The DSO column 11 is preferably a tray or plate column. The DSO column 11 is maintained at a significantly lower pressure than the incoming aqueous solution (preferably less than 0.15 MPa) so that the volatile metal species, syngas and residual organic solvent are evaporated from the aqueous solution as soon as it enters the column 11. And form a gas stream that moves from the inlet 13 to the top 15 of the column 11.

The DSO column 11 may be filled with an aqueous solution except for the overhead space 19 near the top 15 of the DSO column 11. The DSO column 11 may have a bottom outlet 21 through which degassed, stripped, oxidized aqueous solution can be discharged from the DSO column 11. The aqueous solution recycle feed tube 23 may extend from near the bottom 17 of the DSO column 11 to near the top 15. The aqueous solution entering the DSO column 11 moves from the inlet 13 toward the bottom 17 of the DSO column 11. Some of the aqueous solution at the bottom 17 of the DSO column 11 may be discharged from the DSO column 11 through the bottom outlet 21, and some of the aqueous solution may be introduced into the recycle feed pipe 23. A pump 25 may be used to force injection into the aqueous solution from the bottom 17 of the column 11 to the top 15 near the recycle feed conduit 23. The aqueous solution entering the DSO column 11 from the recycle feed pipe 23 may then move downward through the column 11 to the bottom 17 of the column 11.

Air and nitrogen may be injected into the DSO column 11 through ports 27 and 29 at the bottom 17 of the column 11, respectively. The air, nitrogen and gas streams travel upward through column 11, gather in overhead space 19, and exit the column 11 through gas outlet 31. Air and nitrogen oxidize and strip the aqueous solution as it moves upstream with the downwardly moving aqueous solution.

The aqueous solution entering the column 11 from the recycle feed duct 23 contacts the gas stream moving upward from the inlet 13 and separates the volatile metal species from the gas stream. The aqueous solution flowing into the column 11 from the recycle feed pipe 23 is degassed from carbon monoxide, syngas and residual solvent and is rich in oxygen and nitrogen. The aqueous solution entering the column 11 from the recycle feed duct 23 serves to oxidize the gas stream traveling upwards from the inlet 13 and at least partially to oxidize the volatile metal species. The length of the column from the inlet 13 to the point where the aqueous solution is reintroduced to the column through the recycle feed duct removes almost all volatile metal species and their reaction products from the gas stream before the gas stream reaches the overhead space 19. It is preferred to be long enough to provide sufficient contact time between the aqueous solution and the gas stream for this purpose.

A gas recovery stream, oxygen and nitrogen, exiting column 11 through gas outlet 31 is then compressed in a compressor (not shown) and a solvent recovery system (not shown) recovering any residual solvent present in the gas stream. Cooling with low temperature saline. Since the gas stream contains little or no volatile metal species and / or reaction product (s) thereof, little or no solids precipitate in the piping, compressors or solvent recovery systems.

The aqueous solution exiting the column through the bottom outlet 21 may be passed through an acid ion exchange resin bed (not shown) to remove oxidized metal species soluble in the aqueous solution. The aqueous solution can then be passed through a hydrogenation reactor (not shown) to hydrogenate the hydroformylation reaction product, preferably HPA, to a hydrogenation product, preferably PDO.

Referring now to FIG. 2, another preferred embodiment of carrying out the method of the present invention is described. A carbon monoxide / syngas pressurized aqueous solution under a pressure of at least 1 MPa containing a metal species derived from a carbonylation catalyst, a hydroformylation product, carbon monoxide, syngas and residual organic solvent, was placed near the top 37 of the DSO column 33. Inlet 35 may be injected into a degasser-stripper-oxidizer (DSO) column 33. The aqueous solution is preferably an aqueous extract of a hydroformylation reaction carried out using a carbonylation catalyst, most preferably a cobalt carbonyl catalyst. The DSO column 33 is preferably a tray or plate column. The DSO column 33 is maintained at a significantly lower pressure than the incoming aqueous solution (preferably less than 0.15 MPa) so that as soon as carbon monoxide, volatile metal species, syngas and residual organic solvent enter the column 33, Instantaneous evaporation and gathers in overhead space 39 near the top 37 of DSO column 33 to form a gas stream exiting column 33 through gas outlet 41.

The DSO column 33 is preferably filled with an aqueous solution except for the overhead space 19. The aqueous solution entering the DSO column 33 moves from the inlet 35 toward the bottom 43 of the DSO column and is discharged from the column 33 through the bottom outlet 45. Air and nitrogen may be injected into the DSO column 33 through ports 47 and 49 at the bottom 43 of the DSO column 33, respectively. Air and nitrogen oxidize and strip the aqueous solution as it moves up through column 33 in countercurrent with the aqueous solution. Air and nitrogen are collected in overhead space 39 together with the gas stream and exit the column 33 through the gas outlet 41 together with the gas stream. Oxygen in the air acts to oxidize the gas stream upon contact with the gas stream.

Air, nitrogen and gas streams are directed from the gas outlet 41 toward the venturi scrubber 51. Cooling water, preferably having a temperature of 10 to 15 ° C., is also led to the venturi scrubber 51, where the coolant stream and the gas stream in the scrubber 51, air and nitrogen are contacted. The coolant stream separates the volatile metal species from the gas stream, air and nitrogen. The gas stream, air and nitrogen are then led from the venturi scrubber 51 to a compressor (not shown) and then to a condenser (not shown), and a brine solution cooled in the condenser is used to form residual hydroformylation from the gas stream. Solvent is separated. After contacting the gas stream, water can be led out of scrubber 51 as a wastewater stream and passed through a filter (not shown) to remove solids from the water and then circulate back to scrubber 51.

The aqueous solution exiting column 33 through bottom outlet 45 may be passed through an acid ion exchange resin bed (not shown) to remove oxidized metal species soluble in the aqueous solution. The aqueous solution can then be passed through a hydrogenation reactor to hydrogenate the hydroformylation reaction product, preferably HPA, to a hydrogenation product, preferably PDO.

Example 1

The aqueous solution was continuously hydroformylated with ethylene oxide with synthesis gas (CO and H ₂ ) at 60 ° C. to 100 ° C. temperature, pressure of 7 to 15 MPa in the presence of dicobaltoctacarbonyl catalyst in methoxy-t-butyl ether solvent. The reaction mixture was then prepared by continuous aqueous extraction to produce an aqueous solution. Aqueous extraction was performed at 10 MPa and 20 to 45 ° C. The aqueous solution contained 12 wt% to 35 wt% 3-hydroxypropionaldehyde, 50-200 ppm cobalt, and trace amounts of acetaldehyde, MTBE and 3-hydroxypropionic acid. This aqueous solution was passed through a transparent degasser vessel with a diameter of 5.1 cm, a height of 20.3 cm and a 200 ml half-mark mark. The degasser pressure was maintained in the synthesis gas released from the aqueous solution at reduced pressure, and excess gas was vented from the top of the degasser volume. The pressure was measured by a pressure transducer and adjusted to 0.2-0.3 MPa through an automatic regulating valve at the gas outlet. In a separate pressure transducer, the differential pressure associated with the liquid level of the degasser vessel was measured. The liquid level was controlled by a separate control valve for the liquid exiting the bottom of the vessel.

The liquid flow rate from the degaser vessel was transferred to the top tray of a glass stripper column, a 5.1 cm diameter, non-isolated 10 tray Oldershaw column with a maximum liquid load per tray of 0.48 cm. The bottom of this column was fed back with a mixture of 3% O ₂ in N _{2 at} a liquid flow rate of 14.2 to 56.6 liters / hr flow rate. The aqueous solution supplied at the top of the column was stepped downward along the tray and discharged from the bottom of the column to a cobalt ion exchange removal bed. The stripper column was operated under a total pressure of 0.12 to 0.15 MPa with back pressure control of the stripping gas exiting the top of the column.

The degasser and stripper columns were operated continuously for a period of 5 weeks, when the degasser overhead exhaust pipe was clogged with green solids. Analysis of the solids revealed that the main species was cobalt. Similar brownish green solids were observed at the top of the glass Oldershaw column above the liquid inlet point and again analyzed to identify cobalt.

These results demonstrate that volatile cobalt species are produced during degassing and stripping of aqueous solutions produced by water extraction of hydroformylation mixtures using cobalt carbonyl as catalyst.

Example 2

Direct synthesis of cobalt hydridocarbonyl was carried out involving the reaction of dicobaltoctacarbonyl with pyridine to form an imbalance salt and the addition of this salt to sulfuric acid to form cobalt hydridocarbonyl. Direct synthesis was necessary to produce the volatile cobalt species observed during the degassing and stripping of the aqueous extract of the cobalt carbonyl catalyzed hydroformylation mixture for the purpose of examining various means of capturing volatile cobalt species.

3 g of dicobalt octacarbonyl was dissolved in 20 g of pyridine under a blanket of nitrogen to degas the generated carbon monoxide. This mixture was poured into a nitrogen washed burette. The burette was attached to a 250 ml three-necked flask with an outlet and inlet tube fitted at the end and inserted almost at the bottom of the flask. The top of the burette and the inlet tube were connected via a T tube instrument. A solution of 25 ml of 18 M sulfuric acid and 75 ml of water was cooled to -17.8 to -15 ° C, then injected into a 250 ml three-necked flask under a blanket of nitrogen, and the flask was immersed in an ice bath. The flask was then purged with a 2: 1 mixture of hydrogen / carbon monoxide (“synthetic gas”) at a flow rate of about 300 ml / min. Then, pyridine / dicobalt octacarbonyl solution was added dropwise to the acidic solution in the flask for about 45 to 60 minutes to obtain 1.61 to 1.91 g of cobalt hydridocarbonyl.

Example 3

Example 3 is to show that water, steam, MTBE, DSO bottoms and DSO bottoms are effective for separating cobalt hydridocarbonyl compounds from gas streams. Syngas (CO / H ₂ ) was purged at a flow rate of 3 to 10 ml / min through a 300 ml flask containing cobalt hydridocarbonyl synthesized according to the method described above in Example 2. A gas stream containing cobalt hydridocarbonyl and synthesis gas was transferred to a first trap flask having a dip tube in a trap flask arranged to ensure reliable contact between the gas stream and the contents of the trap flask. The contents of the trap flask were water, methoxy-t-butyl ether, 90 ° C. steam or DSO bottom product, and the DSO bottom product was a mixture of 3-hydroxypropionaldehyde hydroformylation reaction mixture containing a cobalt carbonyl hydroformylation catalyst. The aqueous extract was provided by degassing, stripping and oxidizing. The gas stream was then transferred from the first trap flask to a second trap flask containing 1N potassium hydroxide solution, a highly effective capture liquid for cobalt hydridocarbonyl. The gas stream was injected into the second trap flask using a dip tube so that the gas stream was in tangible contact with 1N potassium hydroxide. When the first trap flask contained water or steam, air was added to the gas stream before the first trap flask. In addition, when the first trap flask contained steam, nitrogen gas was added to the gas stream before the first trap flask. The efficiency of the capture liquid examined was best assessed through the percentage of cobalt removed from the first trap flask relative to the total content of cobalt captured in the first and second trap flasks. The results are shown in Table 1 below.

Table 1

These results are effective for water to capture cobalt from oxidized cobalt hydridocarbonyl feed streams with an efficiency of at least 70%, and MTBE, DSO bottoms and vapors are nearly 100% efficient, with non-oxidized cobalt hydridocarbonyl It is shown to be effective in capturing cobalt from the feed stream.

Example 4

The examples show that mechanical filtration using a microfilter is effective for separating cobalt hydridocarbonyl compounds from a gas stream. Syngas (CO / H ₂ ) was purged at a flow rate of 10 ml / min through a 300 ml flask containing cobalt hydridocarbonyl synthesized according to the method described above in Example 2. A gas stream containing cobalt hydride docarbonyl and synthesis gas was passed through the microfilter. This gas stream was passed through a microfilter into a trap flask containing 1N potassium hydroxide solution, a very effective capture liquid for cobalt hydridocarbonyl. The gas stream was then injected into the trap flask using a dip tube to ensure reliable contact of the 1N potassium hydroxide with the gas stream. Air was added to the gas stream before the microfilter. In the first inspection, the filter was a 2 μm filter. In the second inspection, the microfilter was glass wool.

The efficiency of the filters examined was best assessed through the percentage of cobalt removed from the filter relative to the total content of cobalt trapped in the trap flask. The results are shown in Table 2 below.

TABLE 2

This result shows that the microfilter is effective at capturing cobalt from the oxidized cobalt hydridocarbonyl feed stream with at least 90% efficiency.

Example 5

Example 5 shows that a fixed bed of adsorbent material is effective for separating cobalt hydridocarbonyl compounds from a gas stream. Syngas (CO / H ₂ ) was purged at a flow rate of 10 ml / min through a 300 ml flask containing cobalt hydridocarbonyl synthesized according to the method described above in Example 2. The gas stream containing cobalt hydridocarbonyl and syngas was transferred over a fixed bed of molecular sieve (13X) at a VHSV flow rate of 1200 l / h or 2400 l / h. Two molecular sieve fixed beds were used in conjunction with a timer valve used to disperse the flow of the gas stream at one minute intervals between the two beds. Parallel placement of the bed, which periodically moves volatile cobalt gas over the bed, allowed cobalt to be distributed evenly over the bed. The fixed bed of each molecular sieve was 4 cm in length and contained 0.5 g of 0.5 g of molecular sieve. The gas stream was then moved from a fixed bed of molecular sieve to a trap flask containing 1N potassium hydroxide solution, a very effective capture liquid for cobalt hydridocarbonyl, to measure any cobalt breakage from the fixed bed. The gas stream was then injected into the trap flask using a dip tube to ensure reliable contact of the 1N potassium hydroxide with the gas stream.

Two experiments were performed, one to measure the volatile cobalt adsorption effect of the molecular sieve (13X) fixed bed when the gas stream was not oxidized by air, and the other when the gas stream was oxidized by air. The same effect as above was measured. Air was added to the gas stream before the molecular sieve fixed bed upon oxidation test.

The efficiency of the molecular sieve fixed bed separating cobalt from the gas stream was determined as the percentage of cobalt adsorbed to the molecular sieve relative to the gas stream derived cobalt feed. The results are shown in Table 3 below.

TABLE 3

These results show that fixed bed adsorption with molecular sieves is effective for capturing volatile cobalt from an unoxidized cobalt hydridocarbonyl feed stream and an oxidized cobalt hydridocarbonyl feed stream.

Example 6

This example is a hypothetical example deduced from the results and conclusions of Examples 1 and 3 illustrating the method according to the invention. The aqueous solution was continuously hydroformylated with ethylene oxide with synthesis gas (CO and H ₂ ) at 60 ° C. to 100 ° C. temperature, pressure of 7 to 15 MPa in the presence of dicobaltoctacarbonyl catalyst in methoxy-t-butyl ether solvent. The reaction mixture was then prepared by continuous aqueous extraction to produce an aqueous solution. Aqueous extraction was performed at 10 MPa and 20 to 45 ° C. The aqueous solution contained 12 wt% to 35 wt% 3-hydroxypropionaldehyde, 50-200 ppm cobalt, and trace amounts of acetaldehyde, MTBE and 3-hydroxypropionic acid.

This aqueous solution was passed through a degaser, stripper, oxidizer column, which was degassed and stripped into an oxygen and nitrogen gas stream at a pressure lower than the pressure as it entered the stripper, oxidizer column. The gas stream from the stripped and degassed aqueous solution was transferred to the first trap flask using a dip tube in a trap flask arranged to ensure reliable contact between the gas stream and the contents of the trap flask and the contents of the first trap flask. Silver water, methoxy-t-butyl ether, 90 ° C. steam or DSO bottoms, where the DSO bottoms were stripped and degassed aqueous solution. The gas stream was then transferred from the first trap flask to a second trap flask containing 1N potassium hydroxide solution, a highly effective capture liquid for cobalt hydridocarbonyl. The gas stream was injected into the second trap flask using a dip tube so that the gas stream was in tangible contact with 1N potassium hydroxide. The efficacy of the capture medium was determined by comparing the percentage of cobalt removed from the first trap flask to the second trap flask. The capture medium was effective to capture at least 70 wt% or more of cobalt from the gas stream.

Claims (14)

From the gas stream obtained in the aqueous mixture separated from the hydroformylation reaction mixture, comprising separating the volatile metal species from the gas stream obtained by at least partial degassing of the aqueous mixture separated in the hydroformylation reaction mixture. How to inhibit or prevent the deposition of solids The method of claim 1 wherein the volatile metal species is metal hydridocarbonyl. The method of claim 2, wherein the metal hydridocarbonyl is cobalt hydridocarbonyl or rhodium hydridocarbonyl. The method of claim 1, wherein the gas stream contains ether. 5. The method of claim 4, further comprising compressing and cooling the gas stream after separation of volatile metal species from the gas stream to separate ethers from the gas stream. 6. The process according to claim 1, wherein the aqueous mixture is at least partially degassed by lowering the pressure on the aqueous mixture. 7. The method of claim 1, wherein the oxidant is contacted with the aqueous mixture and the gas stream. 8. The method of claim 7, wherein the oxidant is an oxygen containing gas. The method of claim 1, wherein the volatile metal species is separated from the gas stream by contact of the capture liquid with the gas stream. The method of claim 9, wherein the capture liquid is an aqueous mixture separated from the hydroformylation reaction mixture. The method of claim 9, wherein the gas stream is passed through a filter having a pore size of 2 microns or less before contacting the capture liquid. The method of claim 1, wherein the volatile metal species is separated from the gas stream by passing the gas stream through a filter having a pore size of 2 microns or less. The method of claim 1, wherein the volatile metal species is separated from the gas stream by contacting the gas stream with the adsorbent solid. The method of claim 13, wherein the adsorbent solid comprises molecular sieves.

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